The Effect of Bicortical Contact Length on Stem Subsidence of a Monoblock Tapered Fluted Stem

Introduction Taper fluted stems have been the mainstay of femoral revisions for decades. Quick biological fixation is achieved by bony ongrowth. Monoblock and modular designs have been available, however the renaissance of the monoblock is recent, with now multiple designs available, with less stress shielding and predictable new bone formation. Subsidence, and the potential for subsequent instability is the main fear. Bicortical contact length of at least 20 mm is protective of subsidence in modular designs. Aim of this study was to establish the relevance of bicortical contact length on subsidence with a monoblock design and to review a single surgeon, single implant series from 2015–2022. Material and methods Consecutive patients undergoing revision between January 2015 and December 2022 utilizing the Wagner SL stem at the University of Szeged, were chosen from our database. Radiological follow-up used radiographs at 3, 6, 12 and 24 months. The bicortical contact length, cortical width ratio, and start of bicortical length from the tip of the greater trochanter (GT) was measured and Global Radiological Score (GRxS) was utilized for bone remodelling by two blinded observers. Secondary outcome measures: Oxford Hip Score, Visual Analog Scale for pain. Basic demographics and complications were collected. Results 80 patients were identified, 45 aseptic loosening (AL), 35 periprosthetic fractures (PFF). Average age 69 (range 38–89). FU was over 6 years (76 months (26–126). 26 patients required an extended trochanteric osteotomy (ETO). Subsidence was rare, with only 1 patient over 1 cm. Patients undergoing femoral revision, who had no subsidence (less than 5mm) had a slightly better GRxS: 16.9/20, whilst those with subsidence over 5mm has a GRxS: 15.6/20. Functional results were similar. Bicortical contact length was similar in both groups with an average of over 60 mm. There was no correlation between cortical width ratio and cortical contact distance from the GT and subsidence. Patients who had an ETO showed better GRxS scores. Conclusions proximal femoral bone stock reconstitutes quickly around the Wagner SL stem. Subsidence is rare, and not obviously correlated with bicortical contact length.